(1) Field of the Invention
This invention relates to C.sub.21 -dicarboxylic acid based acyl isethionates and their use as primary anionic surfactants in liquid surfactant systems. The invention also relates to the method of producing the surfactants by the reaction of C.sub.21 -dicarboxylic acid, or a blend of C.sub.21 -dicarboxylic acids and fatty acids, with 2-hydroxyethane sulfonate.
(2) Description of the Prior Art
The fatty acyl isethionates 1 are derived essentially from fatty acid or acid chloride and an alkali metal 2-hydroxyethane sulfonate 2 which in turn is derived from ethylene oxide 3 and an alkali metal bisulfite 4, according to the following reaction sequence. ##STR2##
Although first prepared and developed in Germany during the 1930's under the general name Igepon A.RTM. (U.S. Pat. No. 1,881,172), the acyl isethionates have never been widely used in heavy duty detergents for several reasons. First, until recently cheaper petroleum-derived anionics were readily available. Second, because of the sulfonate-activated ester linkage, the isethionates are not hydrolytically stable at the high pH's often encountered in heavy-duty laundry products. Third, the isethionates are high melting (above 150.degree. C.), waxy (when made with excess fatty acid) and relatively water insoluble, making it very difficult to prepare and handle them except as more expensive powders. Currently, the Igepon A.RTM. type products are consumed almost exclusively in synthetic toilet soap bars where they provide mildness, hardness and foam (U.S. Pat. No. 4,180,470). For this application the isethionates are made with an excess of fatty acid which drives the reaction to completion. Stearic acid is added and the mixture neutralized with alkali to give the soap, which is formed directly into bars. Handling problems are thus avoided.
In U.S. Pat. No. 3,842,119, 2-hydroxypropane-sulfonate derivatives of C.sub.21 -dicarboxylic acid were prepared as lime soap-dispersing agents. These are different from the isethionates and are prepared with a process requiring epichlorohydrin.
It is the general object of this invention to provide novel C.sub.21 -dicarboxylic acid based acyl isethionates and their salts which are highly water soluble and useful in liquid surfactant systems. Another object of this invention is to provide a process for producing the C.sub.21 -dicarboxylic acid based acyl isethionates.
Other objects, features and advantages of this invention will become apparent from the following description of the preferred embodiments.